In a conventional mobile communication system, in the case of setting a dedicated channel, a radio network controller RNC determines a transmission rate of uplink data in consideration for a radio resource of a base station Node-B, an interference amount in an uplink data communication, transmission power of a mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required by an upper-level application, and the like. Then, the radio network controller RNC notifies the determined transmission rate of the uplink data individually to the mobile station UE and the base station Node-B by a message of the Layer 3 (radio resource control layer).
Here, the radio network controller RNC is an apparatus that is located at an upper level of the base station and controls the base station Node-B and the mobile station UE.
In general, in the data communication, it is more frequent that traffic occurs in a bursting manner than in a voice communication and a video telephone communication, and it is primarily desirable to change the transmission rate at a high speed.
However, as shown in FIG. 1, the radio network controller RNC usually controls many base stations Node-B in a centralizing manner, and accordingly, in the conventional mobile communication system, there has been a problem that it is difficult to perform such a high-speed (for example, at approximately 1 to 100 ms) change control for the transmission rate because of the reasons such as a processing load and a processing delay.
Moreover, in the conventional mobile communication system, even if the high-speed change control for the transmission rate can be performed, there has been a problem that implementation cost of the apparatus and operation cost thereof are increased to a large extent.
Therefore, in the conventional mobile communication system, it is usual to perform the change control for the transmission rate in several hundred-millisecond to several-second orders.
Hence, in the conventional mobile communication system, in the case of performing a bursting data transmission as shown in FIG. 2(a), the data is transmitted as shown in FIG. 2(b) while permitting a low speed, a high delay, and low transfer efficiency, or the data is transmitted as shown in FIG. 2(c) while ensuring a radio resource for a high-speed communication and permitting waste of a radio bandwidth resource and a hardware resource in the base station during an open time.
Note that, in FIG. 2, both of the above-described radio bandwidth resource and hardware resource apply to a radio resource of an axis of ordinates.
In this connection, in the “3GPP” and the “3GPP2” which are the international standardization organizations of the third-generation mobile communication system, there has been studied a high-speed radio resource control method in the Layer 1 and the MAC sublayer between the base station and the mobile station for the purpose of effectively utilizing the radio resource. Hereinafter, such a study and a function thus studied will be generically referred to as “Enhanced Uplink”.
The radio resource control method studied in the “Enhanced Uplink” is broadly classified into two, and a description will be briefly made below of the classified methods.
As the first radio resource control method, the “dedicated rate control” is being studied. In the “dedicated rate control”, the base station Node-B determines the transmission rate (or maximum allowable transmission rate) of the uplink data in each mobile station UE at every predetermined timing, and notifies the determined transmission rate (or maximum allowable transmission rate) to each mobile station UE, thereby performing the change control for the transmission rate of the uplink data in each mobile station UE. The mobile station UE designated by the base station Node-B transmits the uplink data at the determined transmission rate (or transmission rate within a range of the maximum allowable transmission rate). Here, in the “dedicated rate control”, there is studied a method of not giving transmission opportunities to all the mobile stations UE being connected to the base station Node-B every time but sequentially giving the transmission opportunities only to a part of the mobile stations.
As the second radio resource control method, the “common rate control” is being studied. In the “common rate control”, the base station Node-B notifies a transmission rate of the uplink data, which is common to the mobile stations UE under communication therewith, or necessary information for calculating the transmission rate (hereinafter, “the transmission rate or necessary information for calculating the transmission rate” will be referred to as “transmission rate information” in a lump) to the mobile stations UE, and each of the mobile stations UE determines the transmission rate of the uplink data in each mobile station UE concerned based on the notified transmission rate information.    (Non-Patent Document 1) 3GPP TR 25.896 v2.0.0 March 2004
However, the change control for the transmission rate of the uplink data in such a radio resource control method has had a problem in an operation when soft handover (SHO) is started.
In the conventional mobile communication system, the radio network controller RNC instructs to start the soft handover for the dedicated channel, based on a measurement report from each mobile station UE. In this case, the radio network controller RNC manages the radio resource in each base station Node-B, and accordingly, the radio network controller RNC grasps a usage situation of the hardware resource of each base station Node-B at the point of time when the start of the soft handover is instructed, and such a circumstance is not usually present, where the start of the soft handover becomes impossible since an available hardware resource is insufficient.
However, in the Enhanced Uplink, since each base station Node-B manages the radio resource, the radio network controller RNC does not grasp the usage situation of the hardware resource of each base station Node-B under the control of the radio network controller RNC.
Hence, even if the radio network controller RNC designates the transmission rate of the uplink data in the case of starting the soft handover, in a base station Node-B that newly takes part in the soft handover, such a situation may possibly occur, where the designated hardware resource cannot be prepared, and the soft handover cannot be started. There has been such a problem.
Moreover, the mobile station UE performs the change control for the transmission rate of the uplink data at every transmission time interval (TTI), and accordingly, there has been a problem that it takes a time for the base station Node-B that newly takes part in the soft handover to grasp the hardware resource to be prepared.